A shale gas is a kind of natural gases remaining in a shale rock layer as a sedimentary rock. Petroleum, natural gas, etc., as existing natural resource exist in a reservoir rock such as a sand stone, lime stone, dolomite, etc., having porosity and permeability, and have congregated collectively in a specific area, while the shale gas is distributed widely in a horizontal direction along a shale rock layer having very small porosity and permeability and thus has a feature of efficient existing resource for a horizontal boring.
As a representative method for extracting shale gas, a fracturing method is referred, generating fractures in shale rock layer by pressure of fluid.
Specially, high pressure fluid prepared by mixing chemical substance such as benzene, water and sand is injected into an oil well and a gas well to generate fractures in a shale rock layer with hydraulic pressure, which is referred as a hydraulic fracturing method or a fracking method.
However, since a huge amount of water needs in a case of existing hydraulic fracturing method, there arise problems that a water source needs to be located nearby to improve efficiency and high development cost is required according to various utility establishments for supplying water and treating waste water.
Further, there arises a problem that nearby rock layer and underground water are contaminated due to contaminated substance produced during fracturing process.
Meanwhile, since a huge amount of LPG needs in a case of a fracturing method using LPG instead of water, there arise problems that it is not efficient in terms of economical aspect and further a risk of a big accident exists due to explosion of LPG in a high pressure state.